Activity dependent plasticity

Question 1

how many layers does the neocortex have

Answer 1

6 layers

Question 2

what is layer IV

Answer 2

thalamo-recipient layer

Question 3

prey vs predator visual anatomy

Answer 3

prey = eyes on side
predator = eyes on the front

Question 4

visual system route

Answer 4

retina
LGN
striate cortex (IV)

Question 5

what stains retinotopic maps

Answer 5

cytochrome oxidase

Question 6

what does optical imaging measure for

Answer 6

amount of oxygenated blood (activity)

Question 7

Sur, Garraghty & Roe (1988)
Turning auditory cortex into visual cortex (Ferret)

Answer 7

lesion collicular pathway
loss of auditory input to MGN
feed optic nerve into LGN and MGN
develops orientation specific neurons in A1 which respond to visual features

Question 8

what is hebbian plasticity

Answer 8

modification of existing connections between neurons

Question 9

criteria to implement hebbian plasticity

Answer 9

activity dependence between pre and post synaptic neurons

input specificity (inputs co-active with post synaptic cells)

cooperativity (multiple inputs at once)

associativity (info from 2 sources can be integrated)

longevity (change should last for a specific period)

Question 10

long term potentiation LTP

Answer 10

artificial hebbian plasticity
tetanus (100Hz) causes LTP

Question 11

(beck at el., 2000)
Input specificity of LTP

Answer 11

Insert 2 electrodes in human hippocampal slice (DG)
Input 1 - baseline and tetanus causes LTP after high frequency stimulation
Input 2 - baseline only

Question 12

AMPA receptor

Answer 12

ionotropic glutamate receptor which allows Na+ ion influx via electrostatic and diffusion movement

Question 13

AMPA R antagonist

Answer 13

CNQX

Question 14

NMDA receptor

Answer 14

coincidence detector/induction mechanism

It is ligand and voltage gated
Blockade via Mg2+ in pore
depolarisation removes Mg2+ blockade
NMDAR antagonist (AP5/APV) blocks LTP induction

Question 15

LTD features

Answer 15

LTD is input specific and dependent on NMDAR like LTP
(fire out of sync lose your link)

Question 16

HFS/LFS of the post synaptic cell

Answer 16

HFS - temporal summation - high 5um Ca2+ - protein kinases increase AMPAR function
LFS - low 1um Ca2+ - protein phosphatase decrease AMPAR function

overstimulation can cause epilepsy/coma

Question 17

ocular dominance

Answer 17

contralateral and ipsilateral inputs segregated in L4 (binocular vision requires C&I integration)
ocular dominance occurs in L4 of primate/striate cortex
autoradiography tracks ocular dominance (retina-LGN-striate cortex)

Question 18

methods to inactivate the retina

Answer 18

Colombian tree frog (epibatidine)
newts and pufferfish/fugu - tetrodotoxin TTX - blocks VGSC
Huberman et al., 2003 - normal eye opening occurs at p1-10 in ferret - segregation occurs in LGN, epibatidine inactivates the retina and causes blurred segregation
spontaneous activity not correlated between the two retina

Question 19

what is needed for segregation zones in mouse SI

Iwasato et al., 2000

Answer 19

NMDAR
CXNR1 KO causes no whisker barrel formation

Question 20

Hubel & Wiesel
monocular deprivation in kittens

Answer 20

monocular deprivation of contralateral eye - open contralateral eye - almost all neurons responsive to ipsilateral eye
strabismus (squint) of contralateral eye - equal distribution of responsive neurons
monocular deprivation of contralateral eye - open contralateral eye and NMDAR blockade - no OD shift

therefore, monocular deprivation causes a shift in organisation in LGN & L4 of V1, LTD like plasticity (use it or lose it)

Question 21

ganglion cell receptive field

Answer 21

centre - positive maximal activity
surround - negative minimal activity
ganglion cells differ in firing APs

Question 22

orientation selectivity

Answer 22

orientation selectivity to experience dependence (Ca2+ dependence) - blocked by NMDAR antagonist APV
feedforward excitation from LGN relay cells and summate to form orientation selectivity and intracortical lateral inhibition

Question 23

critical period
monocular deprivation in cats

Answer 23

5wks (OD shift is reversible in kittens) - monocular deprivation of the contralateral eye and reverse suture - close ipsilateral eye- recovers binocular dominance in contralateral eye

14wks - no plasticity (critical period is closed) recently closed ipsilateral eye is dominant

Question 24

cortical inhibition and the critical period

Answer 24

low cortical inhibition - no plasticity
high cortical inhibition - critical period closes
feedforward GABA inhibition is needed to open the critical period
little inhibition = improper coding = no OD plasticity (hence no critical period)

Question 25

Human Amblyopia

Answer 25

lazy eye - cortical blindness
reduced visual acuity in otherwise healthy and properly corrected eye
no depth perception- prevents employment
2% of UK population is affected
most common cause of vision loss

Question 26

causes of amblyopia

Answer 26

strabismus
cataracts/corneal surgery
anisometropia (differences in the refractive index)

Question 27

amblyopia treatment

Answer 27

patch/atropine eyedrops (punish good eye)
-gain in amblyopic eye in expense of fellow eye
-little/no improvement in binocular vision
-poor compliance & varied outcome
-only effective in early childhood

Question 28

temporary monocular deprivation in cats
amblyopia

Answer 28

deficits in binocular vision is restored
10 days of dark exposure recovers eye depression in cats and fluoxetine (prozac) SSRI antidepressant restores critical period plasticity via reduced inhibition, reopens critical period

Question 29

synaptic scaling experiment

Turrigiano & Nelson, 2004

Answer 29

TTX/CNQX then wash - hyperexcitation
bicuculline then wash - little innervation

potentiation follows depression - requires NMDAR

Question 30

Bienenstock, Cooper & Munro (BCM) theory of synaptic plasticity

Answer 30

reduced cortical activity = reduced LTD and increased LTP
activity dependence = presynaptic neurons strengthens the synapse only if the postsynaptic neuron is activate (vice versa)